1. Field of the Invention
The present invention is in the field of packages for integrated circuit dies, and integrated circuits having such packages. More particularly, the present invention relates to an integrated circuit having a package including a base portion and a cover portion, each of which are fabricated of the same material, and therefore each having a thermal coefficient of expansion matching the other.
2. Related Technology
Integrated circuits are known with packages having a base portion of plastic defining an upwardly open recess into which the circuit die is received. An epoxy encapsulant is received into the package over the circuit die, and a metallic cover, which is usually formed of aluminum, may also be placed over the encapsulant to finish the package and enclose the circuit die. Another version of conventional package structure includes a base portion made of plastic with a downwardly opening cavity for the circuit die. These packages generally include a ceramic cover member for the circuit die cavity. The ceramic cover is generally attached to the base portion using a b-stage epoxy frit, that is, a partially cured epoxy carried in a fibrous fabric carrier.
In each case outlined above, the material mismatch between the cover and base portions of the package causes thermally-induced stresses in the package when the integrated circuit is in operation. That is, the operation of the integrated circuit generates heat which is transferred to the package. Because the base and cover portions of the package have differing coefficients of thermal expansion, they expand and contract at different rates during thermal cycling of the package as the integrated circuit die heats during operation and cools after a period of operation. These stresses are in part transferred to the integrated circuit die itself, and to the interconnect structures between the circuit die and the package. Of course these stresses can cause physical distortions of the package and integrated circuit die, and can cause or contribute to failure of the circuit die or of the interconnect structure of the package, for example.
Such a conventional integrated circuit and package is known in accord with U.S. Pat. No. 4,868,638, issued 19 Sep. 1989, to A. Hirata, et al. The '638 patent is believed to teach a package with a base or carrier member which is fabricated of suitable heat-resistant material. For example, the base may be fabricated of polyphenylene sulphide, polysulphone, polyethersulphone, polyarysulphone, phenol, polyamide, or epoxy resin. A heat sink member is molded into the carrier member, and an encapsulant material may or may not be employed. A plate or cover member, of glass or clear epoxy resin, for example, is joined to the carrier. Another version of this package uses a TAB (tape automated bonding) type of interconnect. However, such a TAB interconnect device may similarly be damaged or dislodged by physical shock and vibration. The mismatch of thermal expansion coefficient between the carrier portion and the cover portion of the package is not addressed by the '638 patent.
Other conventional integrated circuits having packages with base and cover portions made of the same material are seen in U.S. Pat. Nos. 4,142,203, issued 27 Feb. 1979, to R. Dietz; 4,355,463, issued 26 Oct. 1982, to C. Burns; 4,833,102, issued 23 May 1989, to R. Byrne, et al. All of these patents use a ceramic base portion and a ceramic cover portion to form the integrated circuit package, perhaps with other components, such as a heat sink member, added as well. However, in each case the package will have an undesirably high manufacturing cost because of the use of the ceramic material, and associated costly and time-consuming processing steps.
Other teachings for integrated circuit packaging which attempt to deal with the problem of differing thermal coefficients of expansion of the package component parts with little or no success, or which simply ignore this problem, are seen in U.S. Pat. Nos. 4,656,499, issued 7 Apr. 1987, to S. Butt; 4,864,384, issued 5 Sep. 1989, to M. Boudot, et al; and 5,070,041, issued 3 Dec. 1991, to S. Katayama, et al.